Process of producing vinyl chloride polymer with mercapto terminated polyvinylalcohol

Abstract

This process uses, as dispersion stabilizers, (A) a partially saponified polyvinyl alcohol having an average polymerization degree of 300 to 2,000, a saponification degree of 70 to 85 mol %, and a mercapto group at least one terminal ends of its molecule chain, and (B) a hydroxypropylmethyl cellulose having a methoxy substitution of 26 to 30% by weight, a hydroxypropoxy substitution of 4 to 15% by weight, and a viscosity of 5 to 4,000 cP at 20.degree. C. in the state of a 2 weight % aqueous solution, in subjecting a vinyl monomer comprised mainly of vinyl chloride to suspension polymerization in an aqueous medium. A polymer which is high in porosity and will provide a molded item having few fish eyes can be produced in high productivity. Furthermore, since deposition of polymer scale on the inner wall of a polymerization vessel is little, removing the scale is easy and the polymerization vessel can be efficiently used.

Claims

1. A process of producing a vinyl chloride polymer, comprising subjecting vinyl chloride or a mixture of vinyl monomers comprising vinyl chloride to suspension polymerization in an aqueous medium in the presence of a dispersion stabilizer, wherein said dispersion stabilizer comprises:

(A) a partially saponified polyvinyl alcohol having an average polymerization degree of 300 to 2,000 and a saponification degree of 70 to 85 mol %, and having a mercapto group at one terminal end of its molecule chain, and a mercapto group or a hydrogen atom at another terminal end of its molecule chain; and

(B) a hydroxypropylmethyl cellulose having a methoxy substitution of 26 to 30% by weight, a hydroxypropoxy substitution of 4 to 15% by weight, and a viscosity of 5 to 4,000 cP at 20.degree. C. in the state of a 2 weight % aqueous solution.

2. A process according to claim 1, wherein the dispersion stabilizer (A) has an average polymerization degree of 500 to 1,500 and a saponification degree of 75 to 85 mol %.

3. A process according to claim 1, wherein the dispersion stabilizer (A) is a compound represented by the general formula: ##STR2## wherein Z, which may be the same or different, is a mercapto group or a hydrogen atom, provided that at least one Z is a mercapto group, and x and y are each a positive integer.

4. A process according to claim 1, wherein the dispersion stabilizer (B) has a methoxy substitution of 27 to 29% by weight, a hydroxypropoxy substitution of 7 to 10% by weight, and a viscosity of 20 to 100 cP in said state.

5. A process according to claim 1, wherein the ratio (A)/(B) of the dispersion stabilizer (A) to the dispersion stabilizer (B) to be charged is in the range of 95/5 to 1/1 by weight.

6. A process according to claim 1, wherein the total amount of the dispersion stabilizers (A) and (B) to be charged is in the range of 0.02 to 0.5 part by weight per 100 parts by weight of the monomer or the monomer mixture.

7. A process according to claim 1, wherein the mixture of vinyl monomers comprises vinyl chloride and at least one comonomer selected from the group consisting of vinyl esters, acrylic acid and its esters, methacrylic acid and its esters, olefins, maleic anhydride, acrylonitrile, styrene,.alpha.-methyl styrene, and vinylidene chloride.

8. A process according to claim 1, wherein

said partially saponified polyvinyl alcohol as an average polymerization degree of 600, a saponification degree of 80.6 mol % and a mercapto group at one end of its molecule chain; and

said hydroxypropylmethyl cellulose has a methoxy substitution of 29% by weight, a hydroxypropoxy substitution of 10% by weight, and a viscosity of 50 cP at 20.degree. C. in the state of a 2 weight % aqueous solution.